AUD Autodesk Inc.

As filed with the Securities and Exchange Commission on November 15, 2012

File Nos. 333-155395

811-22250

U.S. SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form N-1A

PIMCO ETF TRUST

(Exact name of Registrant as Specified in Charter)

840 Newport Center Drive

Newport Beach, California 92660

(Address of Principal Executive Offices) (Zip Code)

Registrant’s Telephone Number, including Area Code

(866) 746-2606

(Name and Address of Agent for Service)

It is proposed that this filing will become effective:

If appropriate, check the following box:

EXPLANATORY NOTE

This Post-Effective Amendment No. 51 to the Registration Statement of PIMCO ETF Trust (the “Trust” or the “Registrant”) incorporates by reference the prospectus and Statement of Additional Information that are contained in the Trust’s Post-Effective Amendment No. 46, which was filed with the Securities and Exchange Commission on June 7, 2012. This Post-Effective Amendment No. 51 is filed solely for the purpose of designating December 14, 2012 as the new effective date of Post-Effective Amendment No. 46, the effectiveness of which was previously delayed pursuant to Post-Effective Amendment No. 47 to the Trust’s Registration Statement, as filed August 20, 2012, Post-Effective Amendment No. 48 to the Trust’s Registration Statement, as filed September 18, 2012, and Post-Effective Amendment No. 49 to the Trust’s Registration Statement, as filed October 17, 2012. This Post-Effective Amendment does not affect the currently effective prospectus and Statement of Additional Information for the other series of the Trust’s shares.