Why Your SaaS Needs AI Chat in 2026 (Add It in 40 Lines)

70% of new SaaS products in 2026 include AI. Here is streaming chat in 40 lines — 20 for the server, 20 for the client. Server export async function POST ( req : NextRequest ) { const { messages } = await req . json (); const res = await fetch ( " https://api.openai.com/v1/chat/completions " , { method : " POST " , headers : { " Content-Type " : " application/json " , Authorization : `Bearer ${ process . env . OPENAI_API_KEY } ` }, body : JSON . stringify ({ model : " gpt-4o-mini " , messages , stream : true }), }); const stream = new ReadableStream ({ async start ( c ) { const r = res . body ! . getReader (); const d = new TextDecoder (); while ( true ) { const { done , value } = await r . read (); if ( done ) break ; for ( const l of d . decode ( value ). split ( " \n " ). filter ( x => x . startsWith ( " data: " ))) { const j = l . slice ( 6 ); if ( j === " [DONE] " ) { c . close (); return ; } try { const t = JSON . parse ( j ). choices ?.[ 0 ]?. delta ?. content ; if ( t ) c . enq