diff --git a/scripts/lib/transcript-context.js b/scripts/lib/transcript-context.js
index d8df7411a..201861487 100644
--- a/scripts/lib/transcript-context.js
+++ b/scripts/lib/transcript-context.js
@@ -35,6 +35,7 @@ const LARGE_WINDOW_MODEL_MARKER = '[1m]';
 // Checked in order, first match wins. Best-effort and expected to lag new
 // releases; the env override remains the escape hatch for unlisted models.
 const KNOWN_MODEL_WINDOW_TOKENS = [
+  ['claude-opus-5', LARGE_CONTEXT_WINDOW_TOKENS],
   ['claude-fable-5', LARGE_CONTEXT_WINDOW_TOKENS],
   ['claude-mythos-5', LARGE_CONTEXT_WINDOW_TOKENS]
 ];
diff --git a/tests/lib/transcript-context.test.js b/tests/lib/transcript-context.test.js
index 4f95c62b4..1d335f131 100644
--- a/tests/lib/transcript-context.test.js
+++ b/tests/lib/transcript-context.test.js
@@ -188,6 +188,10 @@ test('recognizes claude-mythos-5 as a 1M window from the known-model table (#246
   assert.strictEqual(resolveContextWindowTokens(50000, 'claude-mythos-5'), LARGE_CONTEXT_WINDOW_TOKENS);
 });
 
+test('recognizes claude-opus-5 as a 1M window from the known-model table', () => {
+  assert.strictEqual(resolveContextWindowTokens(50000, 'claude-opus-5'), LARGE_CONTEXT_WINDOW_TOKENS);
+});
+
 test('recognizes dated/prefixed variants of known large-window model ids (#2461)', () => {
   assert.strictEqual(resolveContextWindowTokens(50000, 'us.anthropic.claude-fable-5-20260115-v1:0'), LARGE_CONTEXT_WINDOW_TOKENS);
 });