Antigravity Agent 09-2026: Migrate Before October 5

Google released the managed agent identifier antigravity-preview-09-2026 on September 17 and set a hard shutdown date of October 5, 2026 for antigravity-preview-05-2026, after which any application, scheduled workflow, or CI pipeline still calling the old version will fail with a "version no longer supported" error and no fallback. Migrating is a two-minute agent-string swap for code that only reads output_text or model_output from a remote sandbox, but code running locally or parsing function_call steps must first handle three breaking changes: tool parameters renamed from snake_case to PascalCase, write_file switching from full-file rewrites to StartLine/EndLine/NewContent line-range patches, and the addition of the find_by_name and grep_search tools. Google warns that swapping the agent string without fixing the tool surface runs without error but silently returns wrong data.

Google released antigravity-preview-09-2026 on September 17 and gave antigravity-preview-05-2026 a hard shutdown date of October 5, 2026 . Any application, scheduled workflow, or CI pipeline still calling the old agent version will stop working on that date with a “version no longer supported” error — no warning, no fallback, no grace period. How painful the fix is depends entirely on how deeply your code touches the agent’s tool output. What antigravity-preview Is and Why This Affects More Codebases Than You Think The antigravity-preview- strings are managed agent identifiers for Google’s Interactions API — the client.interactions.create call in the Antigravity SDK https://ai.google.dev/gemini-api/docs/antigravity-agent . They’re distinct from the CLI version you install locally. When you call the managed agent, Google runs the full agentic loop on its infrastructure and streams steps back to your code. The agent string is how you pin which behavior you get. The catch: several popular project scaffolds and Antigravity-based tools shipped with antigravity-preview-05-2026 hardcoded as their default. If you adopted one of those projects and never looked at the agent string, you may be exposed without knowing it. Run grep -r "antigravity-preview-05-2026" . in your project now. Are You on the Easy Path or the Hard One? Your migration complexity depends on what you do with the agent’s output: - Remote sandbox, reading output text or model output only: Change the agent string to antigravity-preview-09-2026 . You’re done. This takes two minutes. - Local environment or parsing function call steps: You have three breaking changes to address in the tool surface before you flip the string. If you’re in the second group and simply swap the agent string without fixing the tool surface, your code will run without error but silently return wrong data. That is worse than an obvious crash. Breaking Change 1: PascalCase Parameters Every built-in tool parameter has been renamed from snake case to PascalCase . file path becomes FilePath . start line becomes StartLine . max depth becomes MaxDepth . The change is uniform and mechanical, but it is a silent failure — code that reads step.parameters "file path" returns None rather than raising an exception immediately. Before 05-2026 function call step : { "tool": "read file", "parameters": { "file path": "src/auth.py", "start line": 10, "end line": 50 } } After 09-2026 function call step : { "tool": "read file", "parameters": { "FilePath": "src/auth.py", "StartLine": 10, "EndLine": 50 } } Audit every place your code reads from step.parameters and update the key strings. Breaking Change 2: File Edits Are Now Line-Range Patches The bigger behavioral shift is in how the agent writes files. In 05-2026 , a write file call contained the full file contents — the agent rewrote the entire file on every edit. In 09-2026 , the agent sends targeted patches: a StartLine , an EndLine , and a NewContent block that replaces only those lines. Before 05-2026 write file : { "tool": "write file", "parameters": { "file path": "src/auth.py", "content": "...entire 300-line file..." } } After 09-2026 write file : { "tool": "write file", "parameters": { "FilePath": "src/auth.py", "StartLine": 45, "EndLine": 52, "NewContent": " return validate token token \n" } } If your executor still handles writes by replacing the full file content, you will overwrite hundreds of lines with an eight-line patch. Implement line-range merge logic before you deploy the new version. Beyond compliance, the change is worth adopting — full-file rewrites were slow for large files and produced unreadable diffs. Line-range patches are faster, cheaper, and auditable. What’s New: find by name and grep search Two new built-in tools ship in 09-2026 : find by name SearchDirectory, Pattern, MaxDepth and grep search SearchPath, Query, IsRegex . These replace the shell commands the agent previously ran itself for file search, reducing the class of bugs that came from edge-case escaping on paths with spaces or special characters. Not a breaking change — these are additive — but they are worth using if you build custom tool handlers. Migration Checklist 1. Find the old version string: grep -r "antigravity-preview-05-2026" . — every match is a migration target. 2. Update the agent string: Replace with antigravity-preview-09-2026 in every config, environment variable, and hardcoded call. 3. Update function call parameter keys: If you parse step.parameters , rename all snake case keys to PascalCase. A global search-and-replace on your parameter key strings is the fastest approach. 4. Update file write handling: Replace full-content write logic with a line-range merge implementation. Read the current file into memory, apply the StartLine / EndLine / NewContent patch, write back. 5. Test before October 5: Run your agent against staging with the new version string. Confirm writes produce correct output and parameter reads return expected values. The official deprecation timeline is tracked in the Gemini API changelog https://ai.google.dev/gemini-api/docs/changelog . Complete agent reference documentation is at ai.google.dev/gemini-api/docs/antigravity-agent https://ai.google.dev/gemini-api/docs/antigravity-agent . If you missed the Gemini CLI to Antigravity CLI transition earlier this year, the Antigravity changelog https://antigravity.google/changelog/ covers the full history. For background on what changed when Gemini CLI was retired, see Google Antigravity CLI: What Changed When Gemini CLI Died https://byteiota.com/antigravity-cli-gemini-successor/ .