[Antigravity] Gemini 3.8 Flash outputs raw string calls (:call:default_api:...) instead of executing tool calls

Google Antigravity
1

Environment:

  • Platform: Google Antigravity

  • Model: Gemini 3.8 Flash

  • OS: Windows

Summary: While using Antigravity for code editing and project assistance, Gemini 3.8 Flash frequently outputs raw tool invocation strings directly into the chat response instead of triggering the actual tool execution mechanism. As a result, no files are modified or read, and the raw text is left inert in the conversation.

Symptoms:

  • The model emits pseudocode/internal syntax starting with :call:default_api:....

  • Tools like replace_file_content and view_file are displayed as text blocks instead of performing their respective file operations.

  • The workflow stalls because the client assumes the turn completed without pending executions.

Examples of inert raw outputs:

Example 1 (replace_file_content failure):

Plaintext

:call:default_api:replace_file_content{AllowMultiple:false,Description:Restaura e exibe a janela do Prisma Connector automaticamente quando o Host é assumido por outro computador.,EndLine:735,Instruction:Wire controller.on_host_taken_over in main() to show and restore the window,ReplacementContent:    def get_window():
nonlocal main_window
return main_window
...
TargetFile:c:\Users\pedro.cafure\Documents\antigravity\CuidarSi_Report\prisma_gui.py,toolAction:Adding auto-restore window on host takeover,toolSummary:Auto-restore window on takeover}

Example 2 (view_file failure):

Plaintext

:call:default_api:view_file{AbsolutePath:c:\Users\pedro.cafure\Documents\antigravity\CuidarSi_Report\prisma_gui.py,EndLine:785,StartLine:690,toolAction:Viewing main() in prisma_gui.py,toolSummary:View main() in prisma_gui.py}

Expected Behavior: The model should emit standard function call payloads so Antigravity can parse, validate, and execute file modifications (replace_file_content) and inspections (view_file) natively.

Actual Behavior: The model serializes the function call into the plain text stream, treating it as ordinary message markdown.

2

Hi @CafureG,

Could you please share a few details:

  • The exact reproduction steps to reproduce this issue?
  • The Antigravity version you are using?
  • If it is possible, could you please a screenshot of that particular issue you are facing?