Update claude-api skill: per-SDK doc split, code_execution_20260521, platform-availability, onboarding streamline (#1363)

skills/claude-api/python/claude-api/README.md

@@ -116,9 +116,9 @@ response = client.messages.create(
 )
 ```
 
-### Mid-conversation system messages (beta, model-gated)
+### Mid-conversation system messages (model-gated)
 
-For operator instructions that arrive mid-conversation (mode switches, injected state), append `{"role": "system", ...}` to `messages` instead of editing top-level `system` — this preserves the cached prefix and carries operator authority. Must follow a user message; cannot be `messages[0]`. Unsupported models return a 400 (`role 'system' is not supported on this model`). See `shared/prompt-caching.md` for when to use this vs. top-level `system`.
+For operator instructions that arrive mid-conversation (mode switches, injected state), append `{"role": "system", ...}` to `messages` instead of editing top-level `system` — this preserves the cached prefix and carries operator authority. Must follow a user message (or an `assistant` message ending in server-tool use), and must be either the last entry in `messages` or be followed by an `assistant` turn; cannot be `messages[0]`. Unsupported models return a 400 (`role 'system' is not supported on this model`). See `shared/prompt-caching.md` for when to use this vs. top-level `system`.
 
 ```python
 response = client.messages.create(
@@ -129,8 +129,7 @@ response = client.messages.create(
         {"role": "user", "content": user_message},
         {"role": "system", "content": "Terse mode enabled — keep responses under 40 words."},
     ],
-    extra_headers={"anthropic-beta": "mid-conversation-system-2026-04-07"},
-)
+)  # No beta header needed — use regular client.messages.create
 ```
 
 ---
@@ -258,7 +257,7 @@ If `cache_read_input_tokens` is zero across repeated identical-prefix requests,
 response = client.messages.create(
     model="claude-opus-4-8",
     max_tokens=16000,
-    thinking={"type": "adaptive"},
+    thinking={"type": "adaptive", "display": "summarized"},  # display opt-in: default is omitted (empty thinking text) on Fable 5 / Mythos 5 / Opus 4.8 / 4.7
     output_config={"effort": "high"},  # low | medium | high | max
     messages=[{"role": "user", "content": "Solve this step by step..."}]
 )
@@ -375,7 +374,7 @@ response2 = conversation.send("What's my name?")  # Claude remembers "Alice"
 
 - Consecutive same-role messages are allowed — the API combines them into a single turn
 - First message must be `user`
-- `role: "system"` messages are allowed mid-conversation under the `mid-conversation-system-2026-04-07` beta on supporting models — see § Mid-conversation system messages above
+- `role: "system"` messages are allowed mid-conversation on supporting models (no beta header needed) — see § Mid-conversation system messages above
 
 ---
 
@@ -434,10 +433,39 @@ When `stop_reason` is `"refusal"`, the response includes a `stop_details` object
 
 ```python
 if response.stop_reason == "refusal" and response.stop_details:
-    print(f"Category: {response.stop_details.category}")   # "cyber" | "bio" | None
+    print(f"Category: {response.stop_details.category}")   # e.g. "cyber", "bio", "reasoning_extraction", "frontier_llm", or None — see docs for the full set
     print(f"Explanation: {response.stop_details.explanation}")
 ```
 
+### Refusal Fallbacks (Claude Fable 5) — opt in by default
+
+Fallbacks are **opt-in**: without them a refused request simply stops. Include the server-side `fallbacks` parameter in `claude-fable-5` code by default — on a policy decline the API re-runs the same request on the fallback model inside the same call. A decline before any output isn't billed (a mid-stream decline bills the streamed partial); the rescue bills at the fallback model's own rates, with cache repricing applied automatically.
+
+```python
+response = client.beta.messages.create(
+    model="claude-fable-5",
+    max_tokens=16000,
+    betas=["server-side-fallback-2026-06-01"],
+    fallbacks=[{"model": "claude-opus-4-8"}],
+    messages=[{"role": "user", "content": "..."}],
+)
+
+# Switch points: one fallback block per model that ran and declined this turn
+for block in response.content:
+    if block.type == "fallback":
+        print(f"{block.from_.model} declined; {block.to.model} continued")
+
+# Served-by signal — covers sticky turns, which carry no fallback block.
+# Pair with stop_reason: the fallback model can itself refuse.
+fallback_ran = any(
+    entry.type == "fallback_message" for entry in response.usage.iterations or []
+)
+if fallback_ran and response.stop_reason != "refusal":
+    print(f"Served by {response.model}")
+```
+
+A `stop_reason: "refusal"` on the final response means the whole chain refused. The header must be exactly `server-side-fallback-2026-06-01`; the parameter is rejected on the Batches API and unavailable on Amazon Bedrock, Vertex AI, and Microsoft Foundry — register the client-side `BetaRefusalFallbackMiddleware` on the client there instead. Full semantics (sticky routing, billing, streaming, echoing fallback turns back): `shared/model-migration.md` → Migrating to Claude Fable 5 → `refusal` stop reason.
+
 ---
 
 ## Cost Optimization Strategies

skills/claude-api/python/claude-api/streaming.md

@@ -52,7 +52,7 @@ Claude may return text, thinking blocks, or tool use. Handle each appropriately:
 with client.messages.stream(
     model="claude-opus-4-8",
     max_tokens=64000,
-    thinking={"type": "adaptive"},
+    thinking={"type": "adaptive", "display": "summarized"},  # display opt-in: default is omitted (empty thinking text) on Fable 5 / Mythos 5 / Opus 4.8 / 4.7
     messages=[{"role": "user", "content": "Analyze this problem"}]
 ) as stream:
     for event in stream: