Claude Code 2.1.307 can move your code to the new Claude API version

If you have Claude API code to move to the new API version, update Claude Code and run /claude-api api-version. Claude Code 2.1.307, out Wednesday afternoon, added the command "to move Claude API code to API version 2026-10-21," per the CHANGELOG. It follows Wednesday's API version release, and Anthropic's developer account pointed to it the same day: "You can use the /claude-api skill in Claude Code to update, or walk through each change in the migration guide."

What changed#

Version 2.1.307 reached npm at 4:47 PM ET Wednesday. 2.1.308 followed at 12:19 AM ET Thursday with only "Bug fixes and reliability improvements." When we checked at 5:56 AM ET Thursday, stable, latest and next all pointed to 2.1.308. For 2.1.304 to 2.1.306, see our Oct 21 story.

	Before 2.1.307	2.1.307 and later
Moving code to a new API version	By hand, from the migration guide	/claude-api api-version updates the code, then switches requests to the new version
HTTP MCP tool call when the connection closes mid-call	Could be sent twice	Only read-only or idempotent tools are retried
Tool calls a rule, auto mode, a safety check, a hook or the sandbox stopped, prompted or sent back	No dedicated event in the CHANGELOG	One claude_code.safety_event OpenTelemetry event per call
Unparseable tool call	Ended the turn with an error	Retried up to twice first

Why it matters#

The new API version breaks code that sends sampling parameters, as we covered in what breaks and how to upgrade. @ClaudeDevs said Anthropic plans "to release versions more often so you can handle breaking changes before a new model requires them." Our read: if that happens, a repeatable migration command saves work on every future version, not just this one.

The MCP fix matters if your agents write to other systems. Our read: a tool call sent twice could, for example, open a ticket twice. The CHANGELOG says 2.1.307 "Fixed HTTP MCP tool calls being sent twice when the connection closed mid-call."

How to use it#

1. Run claude update, then claude --version, and confirm 2.1.307 or later.
2. On a new branch, map the work first with this prompt (ours, untested):

Before you change anything, list every file in this repo that calls the Claude API, which SDK and version it uses, and every place that sends temperature, top_p or top_k. Flag any call to a model older than Claude 4.7 on Amazon Bedrock. Then stop and wait for me.

3. Run /claude-api api-version.
4. Read the diff, then run your tests. The migration guide lists the first SDK versions that use 2026-10-21 and says to "upgrade to them," so expect a dependency bump.

Good to know#

• Check the diff against the known breaks. The two to watch are a removed temperature on models such as Claude Sonnet 4.6, and pre-4.7 models on Amazon Bedrock, which can't move. Both are in our Oct 21 story.
• You don't have to move yet. @ClaudeDevs wrote: "2023-06-01 is not deprecated."
• It is a prompt, not a script. The skills docs say bundled skills "are prompt-based." Treat the result as a pull request to review.
• The new event isn't documented yet. At 5:56 AM ET Thursday the monitoring docs, which cover turning on telemetry with CLAUDE_CODE_ENABLE_TELEMETRY=1, had no safety_event, so its fields are unknown. Don't build alerts on it yet.

What to watch: when the monitoring docs describe claude_code.safety_event, and when Anthropic ships its next API version.