diff --git a/CHANGELOG.md b/CHANGELOG.md
index bdd18aa5..847f84d6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,15 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+### Added
+* Add `tnt_crud_storage_nil_bucket_id_compat_total` metric to track operations
+  performed without bucket_ref (legacy router compatibility mode).
+
+### Fixed
+* Fixed storage compatibility with routers < 1.7.0 by handling nil bucket_id
+  in get, update, and delete operations. Now storage skips bucket referencing
+  and logs a rate-limited warning about reduced rebalance safety during rolling upgrades.
+
 ## [1.7.4] - 12-02-26
 
 ### Fixed
diff --git a/README.md b/README.md
index 55cb850f..abcae3a8 100644
--- a/README.md
+++ b/README.md
@@ -153,6 +153,21 @@ router and storage instances.
 >
 > Requests to `vinyl` spaces always run in safe mode regardless of current safe mode status.
 
+> [!IMPORTANT]
+>
+> **Rolling Upgrade Order (< 1.7.0 to >= 1.7.0)**
+>
+> To maintain rebalance safety guarantees, follow this order:
+>
+> 1. Upgrade routers first.
+> 2. Upgrade storages afterwards.
+>
+> Old routers (< 1.7.0) do not send `bucket_id` to storages. If you upgrade storages first,
+> new storages will operate in a compatibility mode with reduced rebalance safety for
+> `get`, `update` and `delete` operations. You will see warnings and
+> `tnt_crud_storage_nil_bucket_id_compat_total` metric increments until all routers are
+> upgraded.
+
 ### Sandbox
 
 The repository provide a simple sandbox application with a test dataset on a single instance.
diff --git a/crud/common/compat_warn.lua b/crud/common/compat_warn.lua
new file mode 100644
index 00000000..57616e84
--- /dev/null
+++ b/crud/common/compat_warn.lua
@@ -0,0 +1,29 @@
+local ratelimit = require('crud.ratelimit')
+local rebalance = require('crud.common.rebalance')
+
+local WARN_INTERVAL_SECONDS = 60
+local WARN_BURST_COUNT = 1
+
+local compat_rl = ratelimit.new({
+    interval = WARN_INTERVAL_SECONDS,
+    burst = WARN_BURST_COUNT,
+})
+
+--- Logs a warning when bucket_id is missing (old router compatibility mode).
+local function log_nil_bucket_id(operation, space_name, engine)
+    local msg = string.format(
+        "crud.%s_on_storage called without bucket_id. " ..
+        "Old router compatibility mode is active: bucket_ref is skipped, " ..
+        "rebalance safety is reduced. Please upgrade routers to restore full guarantees. " ..
+        "(space=%q engine=%q)",
+        operation, space_name, engine
+    )
+
+    compat_rl:log_warn(msg)
+
+    rebalance.inc_nil_bucket_id_compat(operation, engine)
+end
+
+return {
+    log_nil_bucket_id = log_nil_bucket_id,
+}
diff --git a/crud/common/rebalance.lua b/crud/common/rebalance.lua
index 8d3e21d5..d84c311f 100644
--- a/crud/common/rebalance.lua
+++ b/crud/common/rebalance.lua
@@ -17,6 +17,7 @@ local rebalance = {
     _metrics = {
         safe_mode_enabled_gauge = nil,
         router_cache_clear_ts_gauge = nil,
+        nil_bucket_id_compat_counter = nil,
     },
 }
 
@@ -155,9 +156,25 @@ function rebalance.init_storage_metrics()
             'tnt_crud_storage_safe_mode_enabled',
             "is safe mode enabled on this storage instance"
     )
+    rebalance._metrics.nil_bucket_id_compat_counter = metrics.counter(
+            'tnt_crud_storage_nil_bucket_id_compat_total',
+            "count of storage operations performed with skipped bucket_ref (legacy router compatibility mode)"
+    )
     metrics.register_callback(rebalance._metrics.storage_callback)
 end
 
+function rebalance.inc_nil_bucket_id_compat(operation, engine)
+    if not has_metrics_module or not rebalance._metrics.nil_bucket_id_compat_counter then
+        return
+    end
+
+    rebalance._metrics.nil_bucket_id_compat_counter:inc(1, {
+        operation = operation,
+        engine = engine,
+        safe_mode = rebalance.safe_mode_status() and 'enabled' or 'disabled',
+    })
+end
+
 function rebalance._metrics.router_callback()
     if not rebalance._metrics.router_cache_clear_ts_gauge then return end
     rebalance._metrics.router_cache_clear_ts_gauge:set(rebalance.router_cache_clear_ts)
diff --git a/crud/delete.lua b/crud/delete.lua
index a8d7f087..b4e79ce3 100644
--- a/crud/delete.lua
+++ b/crud/delete.lua
@@ -2,6 +2,7 @@ local checks = require('checks')
 local errors = require('errors')
 
 local call = require('crud.common.call')
+local compat_warn = require('crud.common.compat_warn')
 local const = require('crud.common.const')
 local utils = require('crud.common.utils')
 local sharding = require('crud.common.sharding')
@@ -20,7 +21,7 @@ local CRUD_DELETE_FUNC_NAME = utils.get_storage_call(DELETE_FUNC_NAME)
 
 local function delete_on_storage(space_name, key, field_names, opts)
     dev_checks('string', '?', '?table', {
-        bucket_id = 'number|cdata',
+        bucket_id = '?number|cdata',
         sharding_key_hash = '?number',
         sharding_func_hash = '?number',
         skip_sharding_hash_check = '?boolean',
@@ -44,9 +45,16 @@ local function delete_on_storage(space_name, key, field_names, opts)
         return nil, err
     end
 
-    local ref_ok, bucket_ref_err, unref = bucket_ref_unref.bucket_refrw(opts.bucket_id, space.engine)
-    if not ref_ok then
-        return nil, bucket_ref_err
+    -- Skip bucket reference if bucket_id is not provided to support old routers.
+    local unref = nil
+    if opts.bucket_id ~= nil then
+        local ref_ok, bucket_ref_err, unref_func = bucket_ref_unref.bucket_refrw(opts.bucket_id, space.engine)
+        if not ref_ok then
+            return nil, bucket_ref_err
+        end
+        unref = unref_func
+    else
+        compat_warn.log_nil_bucket_id('delete', space_name, space.engine)
     end
 
     -- add_space_schema_hash is false because
@@ -58,9 +66,11 @@ local function delete_on_storage(space_name, key, field_names, opts)
         fetch_latest_metadata = opts.fetch_latest_metadata,
     }, space, key)
 
-    local unref_ok, err_unref = unref(opts.bucket_id, space.engine)
-    if not unref_ok then
-        return nil, err_unref
+    if unref ~= nil then
+        local unref_ok, err_unref = unref(opts.bucket_id, space.engine)
+        if not unref_ok then
+            return nil, err_unref
+        end
     end
 
     return result
diff --git a/crud/get.lua b/crud/get.lua
index 760d8490..7a22971a 100644
--- a/crud/get.lua
+++ b/crud/get.lua
@@ -2,6 +2,7 @@ local checks = require('checks')
 local errors = require('errors')
 
 local call = require('crud.common.call')
+local compat_warn = require('crud.common.compat_warn')
 local const = require('crud.common.const')
 local utils = require('crud.common.utils')
 local sharding = require('crud.common.sharding')
@@ -20,7 +21,7 @@ local CRUD_GET_FUNC_NAME = utils.get_storage_call(GET_FUNC_NAME)
 
 local function get_on_storage(space_name, key, field_names, opts)
     dev_checks('string', '?', '?table', {
-        bucket_id = 'number|cdata',
+        bucket_id = '?number|cdata',
         sharding_key_hash = '?number',
         sharding_func_hash = '?number',
         skip_sharding_hash_check = '?boolean',
@@ -43,9 +44,16 @@ local function get_on_storage(space_name, key, field_names, opts)
         return nil, err
     end
 
-    local ref_ok, bucket_ref_err, unref = bucket_ref_unref.bucket_refro(opts.bucket_id, space.engine)
-    if not ref_ok then
-        return nil, bucket_ref_err
+    -- Skip bucket reference if bucket_id is not provided to support old routers.
+    local unref = nil
+    if opts.bucket_id ~= nil then
+        local ref_ok, bucket_ref_err, unref_func = bucket_ref_unref.bucket_refro(opts.bucket_id, space.engine)
+        if not ref_ok then
+            return nil, bucket_ref_err
+        end
+        unref = unref_func
+    else
+        compat_warn.log_nil_bucket_id('get', space_name, space.engine)
     end
 
     -- add_space_schema_hash is false because
@@ -56,9 +64,11 @@ local function get_on_storage(space_name, key, field_names, opts)
         fetch_latest_metadata = opts.fetch_latest_metadata,
     }, space, key)
 
-    local unref_ok, err_unref = unref(opts.bucket_id, space.engine)
-    if not unref_ok then
-        return nil, err_unref
+    if unref ~= nil then
+        local unref_ok, err_unref = unref(opts.bucket_id, space.engine)
+        if not unref_ok then
+            return nil, err_unref
+        end
     end
 
     return result
diff --git a/crud/ratelimit.lua b/crud/ratelimit.lua
index e39f0a63..32db95c4 100644
--- a/crud/ratelimit.lua
+++ b/crud/ratelimit.lua
@@ -117,6 +117,7 @@ local function log_ratelimited_closure(lvl)
 end
 
 Ratelimit.log_crit = log_ratelimited_closure(S_CRIT)
+Ratelimit.log_warn = log_ratelimited_closure(S_WARN)
 
 return {
     new = ratelimit_new,
diff --git a/crud/update.lua b/crud/update.lua
index 8f8b4dfd..a0381d28 100644
--- a/crud/update.lua
+++ b/crud/update.lua
@@ -2,6 +2,7 @@ local checks = require('checks')
 local errors = require('errors')
 
 local call = require('crud.common.call')
+local compat_warn = require('crud.common.compat_warn')
 local const = require('crud.common.const')
 local utils = require('crud.common.utils')
 local sharding = require('crud.common.sharding')
@@ -20,7 +21,7 @@ local CRUD_UPDATE_FUNC_NAME = utils.get_storage_call(UPDATE_FUNC_NAME)
 
 local function update_on_storage(space_name, key, operations, field_names, opts)
     dev_checks('string', '?', 'table', '?table', {
-        bucket_id = 'number|cdata',
+        bucket_id = '?number|cdata',
         sharding_key_hash = '?number',
         sharding_func_hash = '?number',
         skip_sharding_hash_check = '?boolean',
@@ -44,9 +45,16 @@ local function update_on_storage(space_name, key, operations, field_names, opts)
         return nil, err
     end
 
-    local ref_ok, bucket_ref_err, unref = bucket_ref_unref.bucket_refrw(opts.bucket_id, space.engine)
-    if not ref_ok then
-        return nil, bucket_ref_err
+    -- Skip bucket reference if bucket_id is not provided to support old routers.
+    local unref = nil
+    if opts.bucket_id ~= nil then
+        local ref_ok, bucket_ref_err, unref_func = bucket_ref_unref.bucket_refrw(opts.bucket_id, space.engine)
+        if not ref_ok then
+            return nil, bucket_ref_err
+        end
+        unref = unref_func
+    else
+        compat_warn.log_nil_bucket_id('update', space_name, space.engine)
     end
 
     -- add_space_schema_hash is false because
@@ -73,9 +81,11 @@ local function update_on_storage(space_name, key, operations, field_names, opts)
         }, space, key, operations)
     end
 
-    local unref_ok, err_unref = unref(opts.bucket_id, space.engine)
-    if not unref_ok then
-        return nil, err_unref
+    if unref ~= nil then
+        local unref_ok, err_unref = unref(opts.bucket_id, space.engine)
+        if not unref_ok then
+            return nil, err_unref
+        end
     end
 
     return res, err
diff --git a/test/integration/metrics_test.lua b/test/integration/metrics_test.lua
index 7bc1d3ce..dae2715b 100644
--- a/test/integration/metrics_test.lua
+++ b/test/integration/metrics_test.lua
@@ -7,11 +7,15 @@ local pgroup = t.group('metrics_integration', helpers.backend_matrix({
 }))
 
 local function before_all(g)
+    -- Disable checks to avoid 'fiber is not registered' error.
+    g.old_dev_checks_value = os.getenv('TARANTOOL_CRUD_ENABLE_INTERNAL_CHECKS')
+    helpers.disable_dev_checks()
     helpers.start_default_cluster(g, 'srv_stats')
 end
 
 local function after_all(g)
     helpers.stop_cluster(g.cluster, g.params.backend)
+    os.setenv('TARANTOOL_CRUD_ENABLE_INTERNAL_CHECKS', g.old_dev_checks_value)
 end
 
 local function before_each(g)
@@ -141,3 +145,61 @@ pgroup.test_router_cache_metrics = function(g)
         end
     end)
 end
+
+--- Perform operations with nil bucket_id (emulating old router < 1.7.0).
+pgroup.test_nil_bucket_id_compat_metric = function(g)
+    local has_metrics_module = pcall(require, 'metrics')
+    t.skip_if(not has_metrics_module, 'No metrics module in current version')
+
+    local storage = g.cluster:server('s1-master')
+
+    local common_opts = {bucket_id = nil, skip_sharding_hash_check = true}
+    local ops = {
+        {
+            name = 'get',
+            args = {'customers', 1, nil, common_opts}
+        },
+        {
+            name = 'update',
+            args = {'customers', 1, {{'=', 'name', 'Test'}}, common_opts}
+        },
+        {
+            name = 'delete',
+            args = {'customers', 1, common_opts}
+        },
+    }
+
+    for _, op in ipairs(ops) do
+        storage:call('_crud.' .. op.name .. '_on_storage', op.args)
+    end
+
+    local observed = storage:eval([[
+        return require('metrics').collect({ invoke_callbacks = true })
+    ]])
+
+    local found_metrics = {}
+    for _, m in pairs(observed) do
+        if m.metric_name == 'tnt_crud_storage_nil_bucket_id_compat_total' then
+            table.insert(found_metrics, m)
+        end
+    end
+
+    local function get_metric_value_by_label(metrics_list, op_name, engine_name)
+        for _, m in ipairs(metrics_list) do
+            if m.label_pairs.operation == op_name and m.label_pairs.engine == engine_name then
+                return m.value
+            end
+        end
+        return nil
+    end
+
+    local engine = 'memtx'
+
+    local get_val = get_metric_value_by_label(found_metrics, 'get', engine)
+    local update_val = get_metric_value_by_label(found_metrics, 'update', engine)
+    local delete_val = get_metric_value_by_label(found_metrics, 'delete', engine)
+
+    t.assert_equals(get_val, 1)
+    t.assert_equals(update_val, 1)
+    t.assert_equals(delete_val, 1)
+end
diff --git a/test/integration/simple_operations_test.lua b/test/integration/simple_operations_test.lua
index 4963a5c9..851d72e6 100644
--- a/test/integration/simple_operations_test.lua
+++ b/test/integration/simple_operations_test.lua
@@ -1931,3 +1931,47 @@ pgroup.test_get_invalid_bucket_id = function(g)
         t.assert_str_contains(err.err or err.str, expected_err)
     end
 end
+
+pgroup.before_test('test_storage_compat_nil_bucket_id', function(g)
+    local storage = g.cluster:server('s1-master')
+
+    -- Disable yield checks to avoid 'fiber is not registered' error
+    storage:eval([[
+        local yield_checks = require('crud.common.yield_checks')
+        rawset(_G, '_old_check_no_yields', yield_checks.check_no_yields)
+        yield_checks.check_no_yields = function() end
+    ]])
+end)
+
+pgroup.after_test('test_storage_compat_nil_bucket_id', function(g)
+    local storage = g.cluster:server('s1-master')
+
+    storage:eval([[
+        local yield_checks = require('crud.common.yield_checks')
+        yield_checks.check_no_yields = rawget(_G, '_old_check_no_yields')
+        rawset(_G, '_old_check_no_yields', nil)
+    ]])
+end)
+
+pgroup.test_storage_compat_nil_bucket_id = function(g)
+    local storage = g.cluster:server('s1-master')
+
+    -- get_on_storage with nil bucket_id (emulating old router < 1.7.0)
+    local _, err = storage:call('_crud.get_on_storage', {
+        'customers', 1, nil, {bucket_id = nil, skip_sharding_hash_check = true},
+    })
+    t.assert_equals(err, nil)
+
+    -- update_on_storage with nil bucket_id
+    local _, err = storage:call('_crud.update_on_storage', {
+        'customers', 1, {{'=', 'name', 'UpdatedUser'}}, nil,
+        {bucket_id = nil, skip_sharding_hash_check = true},
+    })
+    t.assert_equals(err, nil)
+
+    -- delete_on_storage with nil bucket_id
+    local _, err = storage:call('_crud.delete_on_storage', {
+        'customers', 1, nil, {bucket_id = nil, skip_sharding_hash_check = true},
+    })
+    t.assert_equals(err, nil)
+end