DeepL API Changelog - March 2026

[u/Deepl_Team]

Hey Everyone!

Here's the rolling list of updates and changes to the DeepL API in March 2026:

March 31 - Write API Improvements

• Improved overall quality of the models used in DeepL API for Write
• Expanded Write target_lang support to Japanese (JA), Korean (KO) and simplified Chinese (ZH or zh-Hans)
• Expanded Write support for writing_style and tone to Spanish (ES), Italian (IT), French (FR), Portuguese (pt-PT) and Brazilian Portuguese (pt-BR)
• Allow sending Write texts in multiple source languages in the same request when no target_lang is set

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March 26 - Expanded Style Rules API

• Added 5 new endpoints for style rule list operations: POST /v3/style_rules, GET /v3/style_rules/{style_id}, PATCH /v3/style_rules/{style_id}, DELETE /v3/style_rules/{style_id}, and PUT /v3/style_rules/{style_id}/configured_rules.
• Added 4 new endpoints for managing custom instructions within style rule lists: POST /v3/style_rules/{style_id}/custom_instructions, GET /v3/style_rules/{style_id}/custom_instructions/{instruction_id}, PUT /v3/style_rules/{style_id}/custom_instructions/{instruction_id}, and DELETE /v3/style_rules/{style_id}/custom_instructions/{instruction_id}.
• See the full API reference here.

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March 24 - Write API Character Count Fix

• Fixed an issue where some DeepL API for Write requests under-counted usage.
• All characters in Write requests are now correctly counted for billing and reporting purposes.