diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2fa642c5..cd7dd412 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -215,6 +215,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/).
 
 ### Fixed
 
+- **AWS/OpenSearch:** the STS account-ID lookup used for post-purchase tagging caches only a successful result, so one throttled or timed-out `GetCallerIdentity` no longer disables tagging for the client's lifetime (#53).
 - **AWS/RDS:** `PurchaseCommitment` refuses an offering whose upfront (`FixedPrice` x count) exceeds the approved recommendation upfront by more than 5%, or that is priced in a non-USD currency; a zero approved upfront is not checked (#53).
 - Bump Go to 1.26.10 to pick up the fix for GO-2026-6809 (crypto/x509), which `govulncheck` now reports against 1.26.9.
 - **AWS/MemoryDB, OpenSearch, Redshift:** `PurchaseCommitment` refuses an offering whose upfront (`FixedPrice` x count) exceeds the approved recommendation upfront by more than 5%, or that is priced in a non-USD currency (MemoryDB offerings carry no currency, so only the recommendation's currency is checked there), or, for MemoryDB, an upfront offering with a zero price or one bought in a China region (cn-north-1, cn-northwest-1), where the assumed USD price is wrong; a zero approved upfront is not checked. All AWS RI price guards (EC2, RDS, MemoryDB, OpenSearch, Redshift) also refuse a NaN or infinite approved upfront (#53).
diff --git a/providers/aws/services/opensearch/client.go b/providers/aws/services/opensearch/client.go
index cfbce7f6..66ff62f3 100644
--- a/providers/aws/services/opensearch/client.go
+++ b/providers/aws/services/opensearch/client.go
@@ -40,12 +40,11 @@ type STSAPI interface {
 
 // Client handles AWS OpenSearch Reserved Instances.
 type Client struct {
-	client      API
-	stsClient   STSAPI
-	accountErr  error
-	accountID   string
-	region      string
-	accountOnce sync.Once
+	client    API
+	stsClient STSAPI
+	region    string
+	accountID string
+	accountMu sync.Mutex
 }
 
 // NewClient creates a new OpenSearch client with purchase-path retry/timeout
@@ -358,22 +357,23 @@ func (c *Client) recoverAlreadyExists(ctx context.Context, token, reservationNam
 	})
 }
 
-// resolveAccountID fetches the caller's AWS account ID via STS and caches it.
+// resolveAccountID fetches the caller's AWS account ID via STS. Only a
+// successful lookup is cached, so a transient failure (throttle, timeout) is
+// retried on the next call instead of sticking for the client's lifetime.
 func (c *Client) resolveAccountID(ctx context.Context) (string, error) {
-	c.accountOnce.Do(func() {
-		if c.stsClient == nil {
-			return
-		}
-		out, err := c.stsClient.GetCallerIdentity(ctx, &sts.GetCallerIdentityInput{})
-		if err != nil {
-			c.accountErr = err
-			return
-		}
-		if out != nil && out.Account != nil {
-			c.accountID = *out.Account
-		}
-	})
-	return c.accountID, c.accountErr
+	c.accountMu.Lock()
+	defer c.accountMu.Unlock()
+	if c.accountID != "" || c.stsClient == nil {
+		return c.accountID, nil
+	}
+	out, err := c.stsClient.GetCallerIdentity(ctx, &sts.GetCallerIdentityInput{})
+	if err != nil {
+		return "", err
+	}
+	if out != nil && out.Account != nil {
+		c.accountID = *out.Account
+	}
+	return c.accountID, nil
 }
 
 // tagReservedInstance constructs the reserved-instance ARN and calls
diff --git a/providers/aws/services/opensearch/client_test.go b/providers/aws/services/opensearch/client_test.go
index 5896d35a..efa94f07 100644
--- a/providers/aws/services/opensearch/client_test.go
+++ b/providers/aws/services/opensearch/client_test.go
@@ -3,6 +3,7 @@ package opensearch
 import (
 	"bytes"
 	"context"
+	"errors"
 	"fmt"
 	"log"
 	"strings"
@@ -1394,3 +1395,27 @@ func TestClient_PurchaseCommitment_Idempotent_RejectedNotFlagged(t *testing.T) {
 	assert.False(t, result.Success)
 	assert.False(t, result.ExistingCommitment)
 }
+
+func TestResolveAccountID_RetriesAfterTransientFailure(t *testing.T) {
+	mockSTS := &MockOpenSearchSTSClient{}
+	client := &Client{stsClient: mockSTS, region: "us-east-1"}
+	acct := "123456789012"
+
+	mockSTS.On("GetCallerIdentity", mock.Anything, mock.Anything).
+		Return(nil, errors.New("throttled")).Once()
+	mockSTS.On("GetCallerIdentity", mock.Anything, mock.Anything).
+		Return(&sts.GetCallerIdentityOutput{Account: &acct}, nil).Once()
+
+	_, err := client.resolveAccountID(context.Background())
+	require.Error(t, err)
+
+	got, err := client.resolveAccountID(context.Background())
+	require.NoError(t, err)
+	assert.Equal(t, acct, got)
+
+	// A successful lookup is cached: no third STS call.
+	got, err = client.resolveAccountID(context.Background())
+	require.NoError(t, err)
+	assert.Equal(t, acct, got)
+	mockSTS.AssertNumberOfCalls(t, "GetCallerIdentity", 2)
+}