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Realtime API instruction limit (16,384 tokens) is too low for production voice agents with tool calling

OpenAI Developer Community April 15, 2026
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Totally get why that feels tight especially when you’re aiming for 99% reliability on a voice agent. That last 10% gap is usually where things get tricky. What’s going on here is the instruction limit you’re hitting is part of the overall context budget. With gpt-realtime-1.5, you actually get a 32k total context window, but about 4k is reserved for output, so the remaining space is shared across everything: * system instructions * conversation history * tool calls and metadata * audio + text inputs So even if instructions feel capped, it’s really the combined load that’s squeezing things. A few folks building similar setups have had better results by: * trimming instructions down to only “always needed” rules * moving less critical logic into tools instead of the prompt * aggressively managing conversation history (summarize or reset when possible) Not ideal, agreed, but it does help stretch that space and improve consistency. There’s also a solid guide on model optimization that walks through ways to rebalance this for voice agents. Worth a look if you haven’t already. Also, you might wanna check the tools usage to see where the tokens are getting eaten. -Mark G.

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