Automatic SMS Chunking for Oversized Messages

Long SMS messages that exceed a route's segment limit now send successfully: enable automatic chunking on a messaging profile and Telnyx splits oversized messages into sequential chunks instead of returning an error.

What's new

• Automatic chunking: Outbound SMS exceeding a route's max segment count are split into ordered child messages, each dispatched after the previous chunk is accepted. Oversized sends return error 40302 when the flag is off.
• One-field activation: Enable auto_chunk_long_messages on any messaging profile with a single API call. The flag is profile-level, with no per-request parameter.
• Encoding-aware splits: GSM-7 messages split on 153-character boundaries and UCS-2 on 67, never mid-character and never inside an escape sequence.
• End-to-end traceability: Each chunk is an independent message with its own message ID, segment count, and delivery receipt. Chunks link via parent_message_id and child_message_id, so you can correlate webhooks that arrive out of order.

Why it matters

Most carriers reject concatenated SMS past 10 segments, which capped how much content you could reliably deliver. Handling that limit yourself means counting segments per encoding, choosing split points, queuing chunks, and matching receipts, and any mistake in that glue code shows up as fragmented or missing messages. Server-side chunking removes the custom code: long-form alerts, reminders, and notifications stay deliverable on capped routes while billing stays predictable, since each chunk bills only its own segment count.

Example use cases

• Operations teams delivering long incident and delivery-status alerts on routes that cap at 10 segments.
• Healthcare and finance apps sending appointment, payment, and compliance reminders without building custom splitting logic.
• Alerting platforms that need oversized sends to dispatch instead of failing with 40302.

Getting started

1. Enable chunking on your messaging profile:

curl -X PATCH https://api.telnyx.com/v2/messaging_profiles/{id} \
  -H "Authorization: Bearer $TELNYX_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"features": {"auto_chunk_long_messages": true}}'

2. Send a message longer than the route's segment limit and watch it dispatch as linked chunks with per-chunk receipts.

Learn more in the SMS chunking docs and the message encoding guide.