A rare instance of speculative development along the Route 128 corridor has found its first tenant.

Deciphera Pharmaceuticals will lease just over 44K SF of office at Anchor Line Partners’ Post at 200 Smith in Waltham. The 10-year, seven-month lease is scheduled to begin in April with an initial rent of $46/SF, according to a May 29 filing with the Securities and Exchange Commission.

The developer will provide up to $2.7M toward building out Deciphera’s office. The pharmaceutical company will also have the right of first offer on a neighboring 30K SF. Neither Deciphera nor Anchor Line were immediately available for comment.

“[The lease] points to the fact life science companies are choosing Waltham and there is this growing life science cluster on Route 128 West,” NAI Hunneman Director of Research Liz Berthelette said.

While there hasn’t been a significant quantity of spec development in the suburbs this cycle, new build-to-suit product has moved the needle for Class-A, Route 128 rents. Existing Class-A product rent averages in the mid-$30s, but Berthelette points to build-to-suit projects like Simpson Gumpertz & Heger’s 200K SF office at Boston Properties’ 20 CityPoint as raising the price ceiling with rents closer to $50 per SF. Deciphera's current executive office is at Boston Properties' 10 CityPoint in Waltham.

“Tenants are demanding highly amenitized, close-in locations like these,” Berthelette said. “That’s more of the ongoing narrative than whether it’s a case of build-to-suit versus spec development.”